1. Field of the Invention
The present invention relates to the preparation of arylaminoaluminums.
2. Description of the Prior Art
Arylaminoaluminums are known materials which are especially useful as catalysts in the ortho-alkylation of aromatic amines with olefins.
Thus, the alkylation of an aromatic amine with olefins, at a temperature of 200.degree. to 400.degree. C. in the presence of aluminum, is described in U.S. Pat. No. 2,762,845. The amine must contain at least one hydrogen atom on the nitrogen atom and at least one hydrogen atom on the aromatic nucleus. If the aluminum-based catalyst can be used in any suitable form, 1 to 2% of aluminum relative to the amine to be alkylated is generally used, and, in practice, the amine and the aluminum source are first brought to a temperature of from 300.degree. to 350.degree. C. When the evolution of hydrogen, caused by the reaction of the aromatic amine with the catalyst to form the corresponding tri(arylamino)aluminum compound is complete, the olefin is then added. The pressure, when the latter is a gas, is on the order of 50 to 300 bar.
The reaction product is then isolated by distillation, either with steam or under vacuum.
Similarly, in Angew. Chem., 68, No. 11, page 387 (1956), referring briefly to the ethylation of aniline in the presence of aluminum, the author points out that aromatic diamines may also be ethylated in the presence of trianilinoaluminum.
Various methods for preparing a trianilinoaluminum type catalyst are also reported in U.S. Pat. No. 2,814,646, one of the simplest consisting of directly contacting the aromatic amine with the aluminum. Also reported in this patent are certain of the advantages associated with the use of a preformed catalyst, in particular the absence of hydrogen evolution which enables a greater partial pressure of the gaseous reagents to be obtained during the actual performance of the alkylation reaction.
It is also known to this art, from U.S. Pat. No. 3,275,690 and the aforesaid Angew. Chem. article, that mercuric chloride is an accelerator of the reaction of aniline with aluminum.
In my laboratory, it has now been observed that the reaction of aniline with aluminum is possible in the absence of accelerator, provided that the reaction is carried out at a high temperature, e.g., greater than 280.degree. C., which necessitates carrying out the reaction in reactors which are resistant to pressure and which is consequently unsatisfactory from an economic point of view.
We have also observed that the subject reaction can be carried out at atmospheric pressure, at the reflux temperature of aniline (approximately 180.degree. C.), in the presence of mercuric chloride, if the reaction is rapid and quantitative. If, however, the paste thus obtained is catalytically active in the alkylation of toluenediamines, for example, it is difficult to handle and the presence of mercuric chloride in such paste tends to contaminate the alkylation products ultimately obtained. Moreover, the cost of mercuric chloride adversely affects the overall cost-effectiveness of the process.
Thus, serious need exists in this art for a novel process for the synthesis of tri(arylamino)aluminums which avoids the disadvantages and drawbacks of the prior efforts in this field.